The present invention relates to a process for improving the permeability of ground formations, which is particularly adapted to the production of high temperature geothermal energy, i.e. when the temperature of the heat conveying fluid reaches or exceeds 200.degree. C.
Two modes of production of high temperature geothermal energy may be distinguished.
The first mode uses natural production of a hot fluid, which limits the application of the process only to favourable sites.
In the second mode, called dry geothermy, there is recovered the sensible heat from rocks located at great depth, and which do not naturally produce fluid at an industrially attractive flow rate.
Heat recovery can then be effected by injecting a cold fluid into a well, this fluid flowing through the hot rock, being heated by contact with this rock and raised up to the ground surface where it is delivered through another well.
However this mode of energy production depends on the permeability of the rocks through which the heat conveying fluid is circulated and unfortunately the rock permeability is poor at great depths.
This permeability can be increased by widening the naturally existing fractures of the ground formations, or fractures by creating in these formations and widening them, or by increasing the permeability of the rock matrix, this permeability increase resulting from the penetration of the fracturing fluid into micro-cracks of the walls of a fracture.